RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 06 April 2017, 11:00-12:00; Duffield Lecture Theatre

Dongwon Kim

"Search for Ultra-faint Milky Way Satellites - End of thesis colloquium"

One of the most pressing issues in the Lambda cold dark matter (CDM) paradigm is the ’’plane of satellite’’ problem: the distribution of observed Milky Way satellite galaxies appears to form a thin polar plane, which is largely inconsistent with the prediction of the Lambda-CDM model, i.e. an isotropic distribution of dark matter sub-halos. This problem was often seen as a consequence of observational biases because many of previously known satellite galaxies were discovered in the Sloan Digital Sky Survey whose survey footprint initially focused on the northern Galactic pole region. Subsequent wide-field surveys to map the southern sky were thus required for an unbiased observational assessment of the standard cosmological model. I present the discovery of five new low-luminosity Milky Way companions from the Sloan Digital Sky Survey, Dark Energy Survey, and Stromlo Milky Way Satellite survey project: two dwarf spheroidal galaxies (Pegasus III & Horologium II) and three star clusters (Kim 1--3). Both Pegasus III and Horologium II, as well as the majority of new dwarf satellite galaxies discovered by other recent studies, turn out tightly aligned with the original plane of satellites defined by previously known satellite galaxies. This result confirms the presence of the plane of satellites throughout the whole sky, which largely conflicts with the previous prediction, and thus calls for a reexamination of the current standard cosmological model.